1. Field of the Invention
This invention relates to a network realized by LAN (Local Area Network) emulation, and more particularly to a LAN emulation server changing over method which allows continuous operation of a network in which LAN emulation servers are redundantly arranged and one of the LAN emulation servers acts as an operational LAN emulation server while the other one or ones of the LAN emulation servers act as a spare LAN emulation server or servers, when a failure occurs with the operational LAN emulation server, without manual changing over of the servers by a maintenance engineer.
2. Description of the Related Art
In a LAN emulation system, a failure of a LAN emulation server which performs address solution and broadcasting between communication terminals is a critical failure by which the entire system is disabled and the network is halted. Where a plurality of LAN emulation servers are disposed on a same network in order to prevent such system down, there is the possibility that the LAN emulation servers may be put into an operative condition simultaneously, resulting in disintegration of the network.
Meanwhile, where a dual construction is realized by a health check by a fixed bus between a plurality of LAN emulation servers arranged on a same network, determination of an operational one and a spare one of the servers must be determined in advance by a maintenance engineer.
For example, a server-client type network system disclosed in Japanese Patent Laid-Open Application No. Heisei 7-182297 includes a plurality of server units which communicate with each other to execute same information processing on the same network, and one of the server units which possesses a network operation right is determined as an operational server unit while the other is determined as a spare server unit. The spare server unit transmits and receives data to and from the operational server unit and establishes synchronism of transaction data to request the operational server unit for data of an operation condition of the same. Then, if an abnormal condition of the operational server unit is detected, then the spare server unit acquires the network operation right and succeeds processing being executed till then from the operational server unit.
However, where the conventional redundancy construction of LAN emulation servers described above is employed, if the plurality of LAN emulation servers which provide equivalent services to each other on the same network operate simultaneously, then there is the possibility that disintegration of the network may occur.
In order to eliminate the possibility described above, the server-client type network system described above must be constructed such that services must be provided only by the operational server unit, and if a failure occurs with the operational server unit, then a maintenance engineer must change over so that the spare server unit may thereafter act as an operational server unit instead.
Further, special means is required to allow communication of information regarding an operation condition of the operational server unit between the operational server unit which is supervised and the spare server unit which supervises.